Nematode Host Meets Bacterial Pathogen

This image shows the nematode host Caenorhbaditis elegans encountering the bacterial pathogen S. marcescens. Natural selection imposed by the co-evolving pathogen led to the evolution and maintenance of bi-parental sex in the host population.

The host and the pathogen were experimentally co-evolved to test the Red Queen hypothesis--that co-evolution with pathogens can select for the maintenance of cross fertilization. Results of research by biologists at Indiana University (IU) support the Red Queen hypothesis prediction as co-evoloving S. marcescens, selected for increased outcrossing in C. elegans.

The IU researchers found that, although sexual reproduction between two individuals is costly from an evolutionary perspective, it is favored over self-fertilization in the presence of co-evolving parasites. Sex allows parents to produce offspring that are more resistant to the parasites, while self-fertilization dooms populations to extinction at the hands of their biological enemies.

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